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How green is mineral wool insulation

AJ__ | Posted in General Questions on

I thought I was settled on using Rockwool batts but as time goes on I question how green it really is. Competitors suggest it has a higher carbon footprint due to the manufacturing process and although it’s green guard certified it does contain some formaldehyde. Is there any unbiased data on this?

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  1. JC72 | | #1

    Green is relative. Rockwool is made partially comprised of waste slag, but yes it takes a lot of energy to manufacture and formaldehyde was/is a non issue.

    Cellulose is probably the greenest cavity insulation but I'd rather take a Grade 1 install of rockwool over Grade 2 cellulose.

    1. Granular | | #4

      ?? Virtually all mineral wool still uses formaldehyde as a binder. Fiberglass manufacturers got rid of formaldehyde binders decades ago but mineral wool manufacturers haven't (although Rockwool does offer a lone 'non-added-formaldehyde' product in very limited quantities/geography).

      1. AJ__ | | #6

        The search for a reasonable combination of "greeness" and indoor air quality has me circling back to fibreglass. Havelock wool looks great but it seems pricey.

      2. JC72 | | #12

        Regardless there's zero evidence that rockwool continues to off-gas formaldehyde when it's installed.

        1. Expert Member
          BILL WICHERS | | #13

          I think it’s rockwool that claims their manufacturing process burns off any residual formaldehyde before the product is finished too. Something used during manufacturing that is not actually present in the final product shouldn't be a problem. It’s similar to pastries that use things like brandy as an ingredient: the alcohol boils off during baking so you don’t get drunk eating the final pastry because the alcohol is no longer present.


  2. mackstann | | #2

    Here's a chart:

    From this article:

    There's been a big debacle over Rockwool's new plant in West Virginia, with a lot of local opposition. The brand new plant is coal fired.

    My personal take is that the different types of insulation exist on a spectrum of badness, and mineral wool is somewhere in the middle. It's not the worst, but not the best either. I use it when greener alternatives aren't practical, but in a perfect world, I'd probably favor cellulose everywhere.

    1. AJ__ | | #5

      That's exactly what I was looking for, thank you.

      Cellulose is proving hard to get for my attic, installers seem scarce and it's logistical challenge to get it to my location-the big box stores don't deliver.

      I would love to use some of the recycled/low carbon exterior products but to my knowledge none of them would be suitable for an area known to have carpenter ants.

  3. charlie_sullivan | | #3

    The chart Nick provided is good. I worry a little that it makes it seem more complicated that it really is. I'd summarize it as:

    Use cellulose or other plant-based insulation where feasible

    For other stuff, mineral wool, fiberglass and EPS are similar on carbon emissions and you should choose on other attributes.

    XPS and HFC blown spray foam are never justified. HFO blown spray foam might be OK in special situations where nothing else works.

  4. Expert Member
    RICHARD EVANS | | #7


    Mineral Wool "Boards" have much higher embodied energy than mineral wool batts due to 3x density and therefore more material.

    Mineral Wool boards of roughly 8 pounds density probably have about the same amount of embodied energy as Type III EPS rigid foam. Mineral Wool batts are much more benign.

    If I had to pick mineral wool, I would definitely choose the ThermaFiber product from Ownens Corning. Rockwool's products use only 20%-40% minimum recycled material, depending upon location. Owens Corning uses a minimum of 70% recycled content! Also, I believe Owen Corning's Joplin, MO plant uses natural gas rather than coal, as Rockwool does (or will with their new WVA plant). You might be able to find Thermafiber options with a local commercial supplier. (Note- I have no affiliation with either company.)

    1. AJ__ | | #8

      Funny you mention Thermafiber because I was looking at that today. A supplier I already use carries it and the price is comparable.

      1. Expert Member
        RICHARD EVANS | | #9

        Alex, I might buy a bag of each and see which one you prefer to work with. I have read online that Thermafiber is a little more difficult to install than rockwool batts.

        1. AJ__ | | #10

          Good idea. They have the board but not the batts. I'm going to look in to the batts more as they have a formaldehyde free version. I'm also going to price out the Havelock wool.

      2. Expert Member
        BILL WICHERS | | #11

        I’ve used thermafiber batts numerous times. They install about the same as the RockWool product, but thermafiber is a little dustier and maybe a bit more brittle (easier to break the batt if you bend it too much). The differences are pretty miner though. I’ve been using thermafiber because it’s cheaper than RockWool branded material for me. There is a bread knife I’ve recommended on here before that works great for cutting these batts.

        The issues with their WVA plant burning coal are pretty minor in reality. Their anticipated coal use is VERY small in comparison to what even a relatively small electric power plant would be using. They’ll likely be required to meet all the same emissions standards too, so it’s not like they’re going to be belching out nasty black smoke. Industry of today is very different than industry of 100 years ago. We had a pretty lengthy discussion of this particular RockWool plant on GBA last year (I think it was last year anyway), so if you’re curious you might try searching the archives for the discussion.

        If you want the all around greenest product, that is probably going to be blown cellulose. The downside is a very different installation methodology. Every product has pros and cons, so I always recommend looking at the entire system — the big picture — any being overly focused on any one particular attribute of any given product, greeness or otherwise. For most homes, you’ll probably find a mix of batts in the walls and blown cellulose in the attic to be the best combination of cost effectiveness and greeness. Spray foam is best reserved for the particular niche applications where it’s the only option.


        1. AlexD2022 | | #14

          Isn't there two insulation areas to consider here, not just wall cavity insulation? If I've settled on blown in cellulose for my wall cavities, what would be the greenest product for my continuous exterior insulation? I've mostly settled on mineral wool boards for my ADU but from reading some the replies here it sounds like EPS might end up being a more responsible choice?

          1. charlie_sullivan | | #15

            EPS might be slightly better on CO2. But depending on your climate, mineral wool might be better on moisture management and thus on durability, and also provides better fire safety.

            I wish someone would build a mineral wool plant that uses solar concentrators for the heat source.

          2. Expert Member
            BILL WICHERS | | #16

            I would use polyiso as my first choice (best R per inch), with EPS as my second choice. I’m not a big fan of rigid rockwool here (sponginess can cause problems with siding install and trim details, and it’s expensive).

            I don’t see solar concentrates as having any possibility of getting the thousand+ degree temperatures and energy quantities needed for production of mineral wool.


  5. AJ__ | | #17

    There’s definitely gap in the market for a low embodied carbon exterior insulation with ant/termite resistance.

    Alex, you might want to see if you can source Sonoclimat Eco4.

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